1. Field of the Invention
The present invention pertains in general to the field of electronic still imaging and, more particularly, to apparatus incorporating digital processing of image signals derived from an electronic image sensor and digital storage of the processed signals.
2. Description Relative to the Prior Art
An electronic still camera employing non-volatile storage of digital image signals is described in copending U.S. patent application Ser. No. 349,566, filed May 9, 1989 now U.S. Pat. No. 5,016,107 dated May 1, 1991, and assigned to the same assignee as the present invention. The electronic still camera disclosed therein employs digital processing of image signals corresponding to a still image and storage of the processed image signals in a removable static random access memory card. An image sensor is exposed to image light and the resultant analog image information is converted to digital image signals. The digital signals are delivered to a multi-image buffer at a rate commensurate with normal operation of the camera. A digital processor operates on the stored digital signals, transforming blocks of the digital signals and encoding the signals into a compressed stream of processed image signals, which are downloaded to the memory card. The digital processor operates at a throughput rate different than the input rate, thereby allowing more efficient image capture and optimum utilization of the camera.
Despite efficient operation of such a camera and the use of compression to reduce the amount of data, high quality digital image files written in the memory card are nonetheless quite large and take significant amounts of time to process due to image size, image resolution, and the nature of the compression process. For example, a 1,280 by 1,024 pixel, 24-bit per pixel image might compress over many seconds to 100 to 300 Kilobytes of storage area. It is often desirable to quickly review the images on the memory card before deciding to transmit, to make a copy, or to retake a picture. The physical time for decompression and display of a high resolution image can be so slow as to interfere with the review process.
The matter of electronic preview has been taken up in a number of prior art disclosures. For instance, in U.S. Pat. No. 4,827,347 an electronic still camera includes a Plurality (twelve) of small displays connected to a like plurality of display/framestores so that pictures can be previewed as a group and then individually retained or discarded. The aforementioned processing time problem, however, is not addressed. In U.S. Pat. No. 4,763,208, an electronic still camera cooperates with playback apparatus that subsamples images recorded on a disk and simultaneously displays the subsampled images as a group on a monitor. While with this construction the contents of the disk can be searched within a shorter time, the subsampled images are unavailable for subsequent review. Research Disclosure item 28618 (p. 71 of the February, 1988 issue) describes a concept for storing video signals from electronically scanned negatives on individual tracks of a video disk while simultaneously storing miniature versions of these pictures in a mosaic frame store. After all the images are recorded on their individual tracks, and the mosaic frame store is accordingly filled, the mosaic-like content of the frame store is itself recorded as a full NTSC frame on a separate track. A similar concept is applied to an all-video picture processing system in U.S. Pat. No. 4,802,019 for rearranging, replacing, or inserting video programs in a sequence of such programs. Each program is characterized by a single frame that is reduced or "squeezed" to one sixteenth its original size and included in a mosaic of like pictures on an index screen. Rearrangement, etc. of the video programs is then made by reference to the index screen. In the latter two systems, the miniaturized pictures are stored together as a video frame. This is of little aid in an all-electronic system in which the pictures are, for example, separately transmitted to a remote location, separately edited, or otherwise used in a way in which continued, rapid review of a particular recorded picture is desirable.